Revert "all: use fixdocs tool to store package documentation in doc.go"

This reverts commit 963877e5f5.

stat/sampleuv/sample.go

@@ -2,6 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Package sampleuv implements advanced sampling routines from explicit and implicit
+// probability distributions.
+//
+// Each sampling routine is implemented as a stateless function with a
+// complementary wrapper type. The wrapper types allow the sampling routines
+// to implement interfaces.
 package sampleuv // import "gonum.org/v1/gonum/stat/sampleuv"
 
 import (